1. Field of the Invention
This invention relates to communications networks. More particularly, this invention relates to methods and systems for upgrading software in ring networks.
2. Description of the Related Art
The meanings of acronyms and certain terminology used herein are given in Table 1.
TABLE 1BLSRBi-directional line switched ringEMSElement management systemFRUField-replaceable unitMPMMain processing moduleNENetwork elementOSIOpen system interconnection modelRIMRing interface moduleRPRResilient packet ringSDHSynchronous digital hierarchySONETSynchronous optical networkSRBCSynchronized ring bandwidth changeSRDLSynchronized ring downloadSWDLSoftware downloadUIMUser interface module
In ring-based networks, scalability and reliability, and in particular the ability to execute non-service affecting (hitless) software upgrades, have become critical issues, particularly for operators of converged, packet-based backbones. A normal software upgrade of a node involves reset of the RIM's (which provide the interface functions between the node and the neighboring spans (segments) of the ring). As used herein, the terms “span” and “segment” are synonymous. Thus, when upgrading several nodes in the same ring in a non-synchronized manner several ring spans can become simultaneously non-operational, which causes a long service outage. Indeed, maintaining network recovery times of 50 ms or less while applying software upgrades to network elements has been a difficult goal to meet at reasonable cost.